Exercise training in chronic obstructive pulmonary disease

Exercise intolerance is a characteristic and greatly troubling manifestatio n of chronic obstructive pulmonary disease (COPD). Patients with moderate t o severe COPD are limited commonly in their abilities to perform usual task s, such as work activities, recreational exercise, and hobbies. When tested in the laboratory setting, patients with COPD typically have higher metabo lic cost of exercise with early-onset lactic acidosis and reduced maximal w ork rate and oxygen consumption compared with healthy persons of comparable age. In the presence of advanced disease, patients experience increasing d ifficulty in performing activities of daily living such as self care and ho usehold maintenance. The resultant inactivity leads to progressive decondit ioning that further increases the sense of respiratory effort related to an y task. As exercise intolerance worsens over time, patients often become pr ogressively homebound and isolated from colleagues, friends, and family mem bers. This sequence of events frequently impairs the patient's quality of L ife (QOL). Concomitantly, some individuals develop worsening depression and anxiety and may withdraw progressively from their usual routines. The basis of exercise intolerance in COPD is complex and multifactorial.(50 ) The physiologic mechanisms of exercise intolerance are discussed in detai l in the article by Nici elsewhere in this issue. In brief, increased airwa ys resistance, ineffective ventilation, hyperinflation and increased elasti c load to breathing, gas exchange abnormalities, and mechanical disadvantag e land in some cases weakness) of the respiratory muscles all contribute to ventilatory limitation during exertion and exercise.(50, 119) Skeletal mus cle dysfunction is another important factor that can contribute to exercise intolerance.(7) This skeletal muscle dysfunction (discussed in detail in t he article by Maltais and colleagues in this issue) is characterized by red uction in muscle mass and strength,(11, 18) atrophy of type I-65,I- 69 and type IIa muscle fibers,(68) reduction in fiber capillarization(133) and oxi dative enzyme capacity,(70, 92) and reduced muscle endurance.(7, 84, 131) B oth resting and exercise muscle metabolisms are impaired.(7, 89, 92) The im paired muscle strength is associated with reduced exercise capacity(55, 62) and increased use of health care resources by patients with COPD.(43) Oxyg en delivery and consumption by the legs is unaffected at submaximal exercis e(89) but may be severely impaired at peak exercise because of complex inte ractions involving central and peripheral factors.(89) Cardiocirculatory, n utritional, and psychologic factors can also affect exercise performance. I n addition to the pathophysiologic processes underlying exercise intoleranc e in COPD, the symptom of dyspnea is a nearly universal complaint and is th e usual cause of exercise limitation cited by the patient.(75) Leg fatigue and discomfort are also common reasons for cessation Of exercise.(75) Importantly, although COPD tin particular, emphysema) is characterized by i rreversible structural alterations in lung architecture, the exercise toler ance of patients with COPD can be improved. Medical therapy and breathing s trategies such as pursed-lip breathing can improve the ventilatory Limitati ons to exercise. Oxygen(143) and nutritional intervention(162) can improve exercise performance. Psychologic support and slow, deep breathing can redu ce anxiety and minimize lung hyperinflation during exercise. Finally, exerc ise training has now been proved to be highly beneficial for patients with COPD. Exercise training has been used in the treatment of patients with COPD sinc e the early 1960s.(26) (100) The use of widely variable exercise protocols in differing types of settings, for patients of varied disease severity and the initial predominance of uncontrolled clinical trials, however, raised some skepticism regarding the clinical benefits of exercise training for th ese persons. In recent years, exercise training has been shown conclusively to improve the exercise tolerance of patients with COPD.* It also improves breathlessness, leg fatigue, and health-related QOL.(5, 6,) (54,) (79,) (8 3,) (129,) (159) In this article, the authors review the data supporting the use of exercise training for patients with COPD. They also discuss the effects of training at different intensities and the mechanisms by which exercise performance improves. It must be noted, however, that although some clinical trials dem onstrating benefits of exercise training have been undertaken in an exercis e laboratory, many others have been conducted in the context of a comprehen sive pulmonary rehabilitation (PR) program. As a result, although exercise training is a crucial core process of PR, the benefits of the training note d in these trials cannot be viewed as separate from the contributing benefi ts of the many other important treatment strategies included in PR, such as patient and family education, training with pacing, energy conservation an d breathing techniques (e.g., pursed-lip breathing), anxiety and dyspnea ma nagement, optimization of oxygen therapy, medical management, and nutrition . Indeed, although not the focus of this review, these additional processes Likely enhance and maximize the benefits of exercise training.(5, 6) As su ch, when possible, exercise training for patients with COPD optimally shoul d be pursued initially in the setting of a formal PR program. It is hoped t hat the techniques and strategies learned in PR will then be transferred in to and continued within the home environment for maintenance of the benefit s achieved over the long term.